Species 10--15
(1 in the flora): worldwide, but absent in cold boreal regions.

The
segregation of Oxyrrhynchiumfrom Eurhynchiumwas initially accepted by many authors, including V. F. Brotherus
(1925). However, it was later placed back into Eurhynchium (e.g., H. Robinson
1962, H. A. Crum and L. E. Anderson 1981).
The phylogenetic analysis of M. S. Ignatov and S. Huttunen (2002)
demonstrated that Eurhynchium
in the broad sense was polyphyletic, and Oxyrrhynchiumbelonged to a different subfamily
different than Eurhynchium
in the strict sense. Oxyrrhynchiumis distinct in having a rough seta
(smooth in Eurhynchium),
and a tendency for subcomplanate foliage, this not
observed in Eurhynchium. Aquatic species closely related to Oxyrrhynchiumare treated as Donrichardsia(cf. S. Huttunen et al. 2007).

Oxyrrhynchiumhiansis
a highly variable species. It ranges from densely foliate, almost tumid
phenotypes to very remotely and complanately-foliate
plants, the latter in shaded habitats. Leaves vary from broadly elliptic and
sometimes almost orbicular to narrowly ovate-triangular. In Florida, plants with multi-spinose costa
were described as O. rappii. However,
R. S. Breen (1963) found this character to be unstable,
sometimes varying along a single stem; H. A. Crum and L. E. Anderson (1981)
also agreed that this name refers to no more than a form of O. hians. EurhynchiumsemiscabrumE.
B. Bartram known from Mexico
and more southern countries is similar to O.
hians and may, at some point, be found in
southern states, especially in Florida.
It differs from O. hians
primarily in its synoicous inflorescence. Despite a broad distribution in the
East and its somewhat weedy nature, O. hiansis mostly absent in the West there it has been
found only twice, in Vancouver, British Columbia, and in California, growing
in man-made habitats (lawns) and should be considered a fairly recent
introduction.